Reaction kinetic modelling of tar cracking in a non-thermal plasma reactor: Model evaluation and reaction mechanism investigation

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Gasification is a process that converts waste into syngas, offering various applications such as fuel, energy, hydrogen production, or further chemicals synthesis. However, tar formation hinders its application due to fouling, corrosion, and catalyst deactivation. Non-thermal plasma (NTP) has emerged as a promising method for tar reforming and cracking, demonstrated through surrogate compounds at the laboratory scale. The scope of this study is to investigate the reaction mechanisms in NTP tar cracking using a zero-dimensional (0D) plasma reactor model with Arrhenius kinetics, aiming to elucidate complex pathways, validate against experimental data, and contribute to the understanding of the reactions. The modelling work utilises a global model to represent NTP. This work collects various reaction kinetics and validates predictions against experimental data. The approach begins with heptane modelling, which is later expanded into (1) toluene in hydrogen gas and (2) a tar mixture (phenol, toluene, and naphthalene) in an oxygen-steam mixture. The model predicts external experimental results with good accuracy, especially at temperatures ranging from 600 to 800 K. The results reveal that radical collisions have a more significant impact on the process than electron impact reactions. Toluene and naphthalene ring-opening reactions occurred when a reactive functional group attacks aromatic double bonds. Finally, the model estimates tar cracking in syngas environment. The low oxygen environment results in secondary tar formation and an abundance of acetylene at the output. Lastly, the assumptions adopted in this study are verified by investigating the impact of plasma and electron temperatures, along with a comparative review of current methodologies in NTP chemistry modelling.